1. Field of the Invention
The invention lies in the area of quality measurement of sound signals, such as audio, speech and voice signals. More in particular, it relates to a method and a device for determining, according to an objective measurement technique, the speech quality of an output signal as received from a speech signal processing system, with respect to a reference signal.
2. Description of the Prior Art
Methods and devices of such a type are generally known. More particularly, methods and corresponding devices, which follow the recently accepted ITU-T Recommendation P.862 (see Reference [1]), are of such a type. According to the present known technique, an output signal from a speech signals-processing and/or transporting system, such as wireless telecommunications systems, Voice over Internet Protocol transmission systems, and speech codecs, which is generally a degraded signal and whose signal quality is to be determined, and a reference signal, are mapped on representation signals according to a psycho-physical perception model of the human hearing. As a reference signal, an input signal of the system applied with the output signal obtained may be used, as in the cited references. Subsequently, a differential signal is determined from said representation signals, which, according to the perception model used, is representative of a disturbance sustained in the system present in the output signal. The differential or disturbance signal constitutes an expression for the extent to which, according to the representation model, the output signal deviates from the reference signal. Then the disturbance signal is processed in accordance with a cognitive model, in which certain properties of human test subjects have been modelled, in order to obtain a time-independent quality signal, which is a measure of the quality of the auditive perception of the output signal.
The known technique has, however, the disadvantage that, for severe timbre differences between the reference signal and the degraded signal, the predicted speech quality of the degraded signal is not correct, or at least unreliable.